When Thomas Fugate graduated from college last year with a degree in politics, he celebrated in a social media post about the exciting opportunities that lay beyond campus life in Texas. “Onward and upward!” he wrote, with an emoji of a rocket shooting into space. His career blastoff came quickly. A year after graduation, the 22-year-old with no apparent national security expertise is now a Department of Homeland Security official overseeing the government’s main hub for terrorism prevention, including an $18 million grant program intended to help communities combat violent extremism. The White House appointed Fugate, a former Trump campaign...